Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

443
FXUS63 KLOT 050740
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
240 AM CDT Fri Jun 5 2026

.KEY MESSAGES...

- Waves of showers and storms are expected starting today and
  lasting through Sunday. Many hours will be dry.

- A few storms this afternoon and tonight may be severe and
  produce torrential downpours.

- Temperatures will be fairly seasonable to slightly above
  average this week before trending warmer next week.

&&

.DISCUSSION...
Issued at 240 AM CDT Fri Jun 5 2026

A recent hand surface analysis augmented by regional 00Z RAOBs
places an expansive reservoir of higher-quality low-level
moisture characterized by dew points in upper 60s to around 70
and mean low-level mixing ratios at or above 12 g/kg west of
the Mississippi River. Several bands of showers and
thunderstorms extend from northern Missouri to central Wisconsin
along the eastern fringe of the low-level moisture axis tied to
low-level isentropic ascent ahead of an upper-level shortwave
lifting into central Iowa. Meanwhile, a secondary upper-level
shortwave is readily evident in overnight GOES-19 water vapor
imagery moving across the Dakotas, and is supporting a
convective system moving into western Minnesota. Finally a
larger and much slower-moving upper-level low is currently
meandering along the US/Mexico border. The overarching weather
pattern is certainly foreboding of a more energetic period
heading our way.


Today:

As the morning progresses, the showers and storms near the
Mississippi River are expected to slide northeastward generally
along and northwest of a line from Mendota to Evanston, IL.
Coverage of thunder may be isolated through the morning hours as
the main instability axis lags to the west. With that said, the
expectation is for episodic downpours amidst a broader rain
shield across northwestern Illinois this morning. Meanwhile,
southeast of the aforementioned line, residual dry low-level air
should limit coverage of rain showers this morning.

An ensemble of CAM-based guidance suggests that an organized
MCV will emerge across southern Iowa later this morning, which
seems reasonable given the ongoing broad zone of active
convection stretching across northern Missouri and the
northeasterly trajectory of the parent shortwave. Southwesterly
flow will be poised to guide the MCV toward the southern
Wisconsin/northern Illinois region by late morning to early
afternoon along the eastern edge of the instability axis. As a
result, do have growing confidence in a period of thunderstorms
this afternoon, favoring areas generally north of Interstate 80.
Locally augmented and veering low-level flow along the southern
side of the circulation (as strong as 40kt from 925 to 700mb
per latest RAP guidance) does raise concern for supercell
structures in the most persistent convective cells should the
MCV remain on the eastern fringe of the instability axis. For
this reason, cannot rule out a few funnel clouds or even a brief
tornado early this afternoon tied to the MCV, which again will
favor areas north of I-80 and perhaps even east of I-39. With
that said, do suspect that convection may struggle to become
rooted to the instability axis given the predominant convective-
scale inflow will be from the relatively more stable air to the
east (though such a limiting factor will not be as much of an
issue by late afternoon, should convection still be ongoing).

For areas south of Interstate 80, today is shaping up to be a
warm and breezy day. At least filtered sunshine should allow for
highs to rise into the low to mid 80s. Mixing into the southern
side of the wind field tied to the MCV will allow for periodic
wind gusts of 25 to 30 mph. Humidity levels will increase
throughout the day, with dew points poised to rise toward 70
degrees by this evening. The air will feel quite a bit heavier
than the past week! Lingering isentropic ascent in the wake of
the MCV may allow for isolated to scattered storms to develop
toward and eventually south of I-80 this evening, though
coverage should not be nearly as high as points to the north.


Tonight:

Forecast confidence lowers after sunset owing to a somewhat
complex regime. Later today, an episode of convection is
expected across Minnesota and central Wisconsin tied to the
aforementioned Dakotas shortwave. Increasing isentropic ascent
ahead of and beneath the left entrance region of a jet max
associated with the wave into the Midwest region, as well as an
approaching subtle 700mb speed max itself advecting a remnant
EML plume eastward from the Plains, should excite a separate
region or two of thunderstorms after dark from central Iowa
toward northern Illinois. While pin-pointing exactly where
thunderstorms will erupt in this kind of nocturnal regime can be
difficult, the latest CAM guidance seems to favor an axis near
and south of Interstate 80 between 9 PM and midnight, especially
across Iowa.

In spite of somewhat marginal deep-layer shear (as the upper-
level jet max will be displaced across central Wisconsin and
Michigan), moisture-laden instability profiles aided by mid-
level lapse rates near 7 to 7.5 K/km will support MUCAPE of 2000
to locally 3000 J/kg. Taken together, the most vigorous
convection may be able to support scattered damaging hail and
winds (a higher coverage being limited by a lack of more
appreciable deep-layer shear). Perhaps more pervasive will be
torrential downpours moving over the same general area, given modest
backward corfidi vector magnitudes (a consequence of a somewhat
weak low-level jet magnitude). Accordingly, do believe there is
a threat for localized flash flooding in the general region
tonight in spite of the recent dry stretch. Note that some
areas, and perhaps even a large portion of our area, will
remain completely dry tonight.


Saturday:

Coverage of overnight showers and storms should wane toward
daybreak owing to the diurnal weakening of the low-level jet and
subsidence in the wake of the overnight shortwave. Currently do
anticipate a fair amount of sunshine by early afternoon, which
should allow for temperatures to warm to the mid to locally
upper 80s. The generally weak low-level pressure gradient and
continued cool Lake Michigan temperatures (in the upper 50s to
lower 60s per the recent OMRLOT product) should allow for a lake
breeze to develop and push inland during the afternoon hours.
The continued humid conditions (dew points in the upper 60s to
lower 70s) will support convective temperatures somewhere in the
upper 80s, setting the stage for isolated to perhaps scattered
"pop-up" diurnal thunderstorms by mid afternoon. Coverage may be
locally higher near the lake breeze given locally stronger low-
level convergence. Most areas should be dry.


Sunday into Monday:

Toward the start of next week, the upper-level low currently
traversing the US/Mexican border will finally begin lifting
northeastward toward the Mississippi River Valley. The (by this
point somewhat stagnant) humid airmass will hence be poised to
support episodes of showers and storms as the upper-level low
approaches and eventually moves overhead. Periods of cloud
cover, as well as onshore flow forced by a surface high pressure
system moving across eastern Canada, will lead to seasonable
temperatures generally close to 80 degrees both days.


Tuesday Onward:

In the wake of the upper-level low, ensemble model guidance
appears steadfast in depicting the development of persistent
troughing across the Pacific Coast and upper-level ridging
across the Midwest and Great Lakes region. As a result,
temperatures should warm throughout next week with highs
climbing into upper 80s to perhaps lower 90s by the weekend.
When combined with the continued humidity, it`ll start to feel
more like summer next week. Will note that there are differences
in the placement of the ridge next week, suggesting that there
may be opportunities for storms (and associated localized
natural air conditioning) in the general region as well.

(Note that the high temperatures in the mid to upper 90s and
associated much higher heat indices being advertised by the NBM
toward the end of next week are not currently supported by input
ensemble data).

Borchardt

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1257 AM CDT Fri Jun 5 2026

Main Concerns:

- Potential for occasional SHRA/TS with associated VSBY
  reductions today and again late this evening-overnight

- Lower CIG trends this morning through this afternoon

- Chance for a north-northeasterly wind shift associated with
  the SHRA/TS threat late this evening-overnight

The long stretch of mainly quiet flying weather will come to an
end over the next 24+ hours. Initial showers and possible embedded
TS in the pre-dawn through mid morning should generally favor
northwest IL/RFD area (PROB30 for TS there), though spotty VFR
showers could develop over the Chicago metro. The overall best
chance for on station TS impacts will be from mid morning
through early to mid afternoon, earliest at RFD, and latest at
GYY. Maintained TEMPO TS mention with similar timing to
previous issuances. After the afternoon activity shifts east,
our next period of interest is late this evening and overnight.
There`s some signal for showers and storms to develop north of
the terminals (possibly over WI) and sag south, accompanied by
an outflow driven wind shift to north or northeast. Introduced
PROB30s at ORD, MDW, and GYY for this window.

South-southwest winds early this morning will become gusty out
of the southwest after daybreak, with some potential for
occasional gusts as high as 25-30 kt in the early to mid
afternoon. Lowest CIGs (lower MVFR to temporary IFR) during
daylight hours today should focus into RFD area, though 2-3kft
AGL CIGs appear probable at times at the Chicago metro
terminals.

Castro

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 10 AM this morning to 7 PM CDT this
     evening for the IL and IN nearshore waters.

&&

$$

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